The climactic
June 1991 eruption of Mount Pinatubo, Philippines, was the largest volcanic
eruption in this century to affect a heavily populated area. Because it was
forecast by scientists from the Philippine Institute of Volcanology and Seismology
and the U.S. Geological Survey, civil and military leaders were able to order
massive evacuations and take measures to protect property before the eruption.
Thousands of lives were saved and hundreds of millions of dollars in property
losses averted. The savings in property alone were many times the total costs of
the forecasting and evacuations.

On the morning of June 15, 1991, Mount Pinatubo on the island of Luzon in the
Philippines exploded in the largest volcanic eruption on Earth in more than
three-quarters of a century. The most powerful phase of this cataclysmic
eruption lasted more than 10 hours, creating an enormous cloud of volcanic ash
that rose as high as 22 miles into the air and grew to more than 300 miles
across, turning day into night over central Luzon. Falling ash blanketed an area
of thousands of square miles, and avalanches of hot ash (pyroclastic flows)
roared down the slopes of the volcano and filled deep valleys with deposits of
ash as much as 600 feet thick.

Villagers fleeing
the vicinity of Mount Pinatubo, Philip-pines, during heavy ash fall from the
volcano's cataclysmic June 15, 1991, eruption. Scientists from the Philip-pine
Institute of Volcanology and Seismology and the U.S. Geological Survey forecast this
eruption, enabling people living near the volcano to evacuate to safety.
The timely forecasts of these scientists saved at least 5,000
lives and prevented property losses of at least $250 mil-lion.
(Photo by Philippe Bourseiller/Jacques Durieux.)

Before the cataclysmic eruption, about 1,000,000 people lived in the region
around Mount Pinatubo, including about 20,000 American military personnel and
their dependents at the two largest U.S. military bases in the
PhilippinesClark Air Base and Subic Bay Naval Station. The slopes of
the volcano and the adjacent hills and valleys were home to thousands of
villagers. Despite the great number of people at risk, there were few casualties
in the June 15 eruption. This was not due to good luck but rather was the result
of intensive monitoring of Mount Pinatubo by scientists with the Philippine
Institute of Volcanology and Seismology (PHIVOLCS) and the U.S. Geological
Survey (USGS).

The first recognized signs that Pinatubo was reawakening after a 500-year
slumber were a series of small steam-blast explosions in early April 1991.
Scientists from PHIVOLCS immediately began on-site monitoring and soon declared
a 10-kilometer- (6-mile-) radius danger zone around the volcano. They were
joined in a few weeks by USGS scientists from the Volcano Disaster Assistance
Program, a cooperative effort with the Office of Foreign Disaster Assistance of
the U.S. Agency for International Development.

Scientists from the U.S. Geological Survey and the
Philippine Institute of Volcanology and Seismology making emergency
repairs to monitoring instruments on Mount Pinatubo, Philippines, with
U.S. Air Force helicopter support, the day before the volcano's
cataclysmic June 15, 1991, eruption. (Photo by MSgt. Val Gempis, U.S. Air
Force.)

The USGS scientists brought with them specially designed, portable
instruments, which the joint Philippine-American team used to quickly set up
monitoring networks on and around Mount Pinatubo. The team also conducted
intensive studies of the volcano's past eruptive history. When the data from
these efforts indicated that a huge eruption of the volcano was imminent, the
joint team issued urgent warnings. These timely forecasts enabled civil and
military authorities to arrange the evacuation of people and aircraft and other
equipment to safe areas before Mount Pinatubo exploded on June 15.

Lives and Property Saved

The USGS and PHIVOLCS estimate that their forecasts saved at least 5,000
lives and perhaps as many as 20,000. The people living in the lowlands around
Mount Pinatubo were alerted to the impending eruption by the forecasts, and many
fled to towns at safer dis tances from the volcano or took shelter in buildings
with strong roofs. Additionally, more than 15,000 American servicemen and their
dependents were evacuated from Clark Air Base prior to the June 15 eruption. In
the eruption, thousands of weaker roofs, including some on Clark, collapsed
under the weight of ash made wet by heavy rains, yet only about 250 lowland
residents were killed. Of the 20,000 indigenous Aeta highlanders who lived on
the slopes of Mount Pinatubo, all but about 20 were safely evacuated before the
eruption completely devastated their villages. Some might have left on their
owntroubled by the steam blasts and earthquakes that preceded the
eruptionbut most would have remained had it not been for the
forecasts and government-led evacuations.

In addition to the many lives saved, property worth hundreds of millions of
dollars was protected from damage or destruction in the eruption. When aircraft
and other equipment at the U.S. bases were flown to safe areas or covered,
losses of at least $200 to 275 million were averted. Philippine and other
commercial airlines prevented at least another $50 to 100 million in damage to
aircraft by taking similar actions. By heeding warnings of hazardous volcanic
ash clouds from Pinatubo, commercial and military pilots avoided severe damage
to their aircraft and potentially saved hundreds of lives. Other commercial
savings are harder to quantify but were probably less than $100 million, and
there is no way to estimate the sentimental or monetary value of the personal
property saved by families.

Cost of Forecasting and Evacuations

PHIVOLCS and USGS scientists spent less than $1.5 million responding to Mount
Pinatubo's reawakening and forecasting its June 15, 1991, eruption, including
salaries, helicopter and other logistical support, and the replacement of
equipment destroyed by the eruption. Their forecasts were made possible by
previous work in the area by PHIVOLCS and by the USGS' mobile monitoring
capability, also available to respond to volcano crises in the United States.
The costs of these earlier efforts can be roughly estimated at $15 million (10
percent of the combined 1980&endash;90 volcano hazards budgets of PHIVOLCS
and the USGS). Additionally, the Philippine and U.S. Governments and
nongovernmental organizations together spent about $40 million to evacuate,
house, and feed local residents and American military personnel and their
dependents.

On June 15, 1991, Mount Pinatubo in the Philippines
erupted cataclysmically, raining volcanic ash over an area of thousands of
square miles and sending high-speed avalanches of hot ash (pyroclastic
flows) roaring down the flanks of the volcano. Falling ash caused
thousands of roofs to collapse, clogged stream channels, made roads
impassable, and created massive cleanup problems (photos). Before the
eruption more than 1,000,000 people lived within 30 miles of the volcano,
including about 20,000 American military personnel and their dependents.
Because forecasts of this powerful eruption by a joint team of U.S.
Geological Survey and Philippine scientists allowed timely evacuations,
fewer than 300 people were killed. (U.S. bases have reverted to Philippine
control since 1991.)

Were These Efforts a Good Investment?

The monitoring of Mount Pinatubo in 1991 and the successful forecasting of
its cataclysmic June 15 eruption prevented property losses of at least $250
million (this figure is intentionally conservative and should be considered a
minimum value). No monetary value has been placed on the more than 5,000 lives
saved, although other cost-benefit analyses have used values from $100,000 to $1
million per life.

Even when the costs of developing the portable monitoring capability and of
the earlier studies of Mount Pinatubo are included, the total costs of
safeguarding lives and property from the volcano's June 15, 1991, eruption were
only about $56 million. The savings in property alone amounted to at least five
times this total investment!

Although savings may not always be as dramatic as those realized at Pinatubo,
many lives can be saved and major property losses avoided in other volcano
crises through similar relatively modest investments in volcano monitoring and
eruption forecasting. The experience gained by scientists during Pinatubo's 1991
eruption crisis is being used by the USGS Volcano Hazards Program in the United
States and by PHIVOLCS in the Philippines to better protect people's lives and
property from the future volcanic eruptions that will inevitably occur.

COOPERATING
ORGANIZATIONS
Armed Forces of the Philippines
National Disaster Coordinating Council, Philippines
Philippine Institute of Volcanology and Seismology
U.S. Agency for International Development
United States Air Force
United States Navy